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CHP launched an investigation after cell phone video was released that shows an officer hitting a woman on a Southern California freeway median. Warning: some may find the video difficult to watch. Beverly White reports for the NBC4 News at 11 p.m. Thursday, July 3, 2014. (Published Friday, July 4, 2014)

The California Highway Patrol is investigating after cellphone video captured an officer repeatedly hitting a woman in the face as she lay flat on her back just off a Los Angeles freeway.

The video titled "Police Brutality?" was shot Tuesday evening from a vehicle entering the eastbound 10 Freeway near La Brea Avenue and posted on YouTube the following day. It runs for 1 minute, 30 seconds and includes footage of the incident in real time and in slow-motion.

The man who shot the footage, David Diaz, a self-described music producer, spoke with NBC4 about what he saw.

"She took a left, and the cop, the CHP ran after her, grabbed her to try to subdue her, and then she you know, kind of tried to shove it off...Was she intoxicated? Was she mentally ill? Possibly," Diaz said.

"The California Highway Patrol (CHP) just became aware of the video today and we are investigating the entire incident," according to the statement. "As a matter of policy, every time there is a use of force by our officers, there is a review conducted to determine whether the use of force was appropriate. That will be done in this case, however, since there is an ongoing investigation, it would be premature to comment on this specific video segment. After the investigation is completed it will be reviewed at multiple levels within the Department."

The CHP did not immediately say what prompted the initial encounter.

The video footage begins as the CHP officer is standing next to a red pick-up truck on the freeway on-ramp. He makes his way across to a concrete median where he follows a woman who is walking there and is carrying a white bag.

Moments later, the officer tries to grab the woman's arm as she appears to resist.

As he tries to gain control over the woman, he throws her to the ground. While the woman is on her back, the officer holds her down and delivers about a dozen hits to her head and upper body in about 11 seconds, according to the video.

"These are like, grown men, on top of you punching you to a point where she could've died out there," Diaz said.

The woman, who was not immediately identified, appears to use her arms and hands to protect her face from the officer's blows. A second man joins the officer to help control the woman as she is placed in handcuffs.

"She was screaming," witness Daina Tate said. "Two men were on her. They had her arms up. She couldn't defend herself. She looked totally helpless and terrified.

"It was shocking, and you can't really call the cops on the cops."

Another witness who did not want to be identified told NBC4 the woman "did not look well, mentally" when she was walking along the freeway.

The woman was "carrying a lot of bags" and was not wearing shoes, only black socks, the witness said.

After she was brought down to the asphalt by the officer, the woman put her arms up "trying to guard herself," the witness said. "She looked terrified...she just looked gone."